Transducers that convert signals from one domain to another are often used in sensors. A common sensor that includes a transducer is a pressure sensor that converts pressure differences and/or pressure changes to electrical signals. Pressure sensors have numerous applications including, for example, atmospheric pressure sensing, altitude sensing, and weather monitoring.
Microelectromechanical system (MEMS) based sensors include a family of transducers produced using micromachining techniques. MEMS, such as a MEMS pressure sensor, gather information from the environment by measuring the change of physical state in the transducer and transferring the signal to be processed by the electronics, which are connected to the MEMS sensor. MEMS devices may be manufactured using micromachining fabrication techniques similar to those used for integrated circuits.
MEMS devices may be designed to function as oscillators, resonators, accelerometers, gyroscopes, pressure sensors, microphones, and/or micro-mirrors, for example. Many MEMS devices use capacitive sensing techniques for transducing the physical phenomenon into electrical signals. In such applications, the capacitance change in the sensor is converted to a voltage signal using interface circuits.
A pressure sensor may also be implemented as a capacitive MEMS device that includes a reference volume and a deflectable membrane. A pressure difference between the reference volume and an external volume, such as the ambient environment in some cases, causes the membrane to deflect. Generally, the deflection of the membrane causes a change in distance between the membrane and a sensing electrode, thereby changing the capacitance. Thus, a pressure sensor measures a pressure difference between the reference volume and an external pressure.
For transducers that interact with an external environment outside the device, such as a pressure sensor, an opening or coupling to the external environment is usually included in the device structure. For example, microphones generally include a sound port and pressure sensors generally include a similar air pressure port. When the device is packaged, such openings or couplings may provide a way for contaminants such as dirt or particles to affect transducers that include such openings.